Cortana, Microsoft's voice-powered personal assistant software that was first unveiled at the Build developer conference in April, is included, too, but only for US customers for now.

Enterprise users can also benefit from new support for digitally encrypted email via S/MIME and improved VPN support.

The Cyan add-on package brings additional features for Lumia device owners, but just which ones depends at least partly on which handset they have.

Owners of all Windows 8 Lumia phones can expect updates to Nokia's suite of photography-related apps, including the Camera app itself, Nokia Creative Studio, and Storyteller. Improvements include UI tweaks, new filters and image enhancement tools, and the ability to share photos as video slideshows via social networks.

In addition, owners of Lumia 520, 525, 620, and 720 handsets will see their devices' turn-by-turn navigation software upgraded from the region-limited Here Drive product to the unlimited, global Here Drive+ version.

Lumia 1520 and Lumia Icon devices will gain improved audio quality for video recording, thanks to the addition of Nokia Rich Recording and Dolby Digital Plus 5.1 sound technologies. Their cameras will also gain continuous autofocus, improved colors, and better low-light performance, and Microsoft's Screen Share technology will allow them to cast content from their devices' screens to connected screens like smart TVs or projectors.

Apps built for the Lumia 1520 and Lumia Icon running Windows 8.1 can also take advantage of the SensorCore SDK Beta, which allows developers to access data about location, number of miles walked, and so on.

The Lumia Cyan update, including Windows Phone 8.1, started rolling out on Tuesday and will make its way around the globe in the coming weeks. Nokia has promised that all Lumia devices that are currently running Windows 8 will receive the update. Older Windows Phone devices, on the other hand, won't – but then, they received no upgrade to Windows Phone 8, either.

Non-Nokia devices running Windows Phone 8 – those paltry few – aren't eligible for the Cyan upgrade, but they should be capable of running Windows Phone 8.1. Whether their manufacturers will actually ship the upgrade, however, remains to be seen. ®